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Microwave drying of spice and herbs

Identification

Key words Spice, herbs, microwave, drying, dehydration, heat sensitive compound, volatile
Latest version 2012/03/29
Completed by FRIP

How does it work?

Primary objective Drying of spices and other biological material like herbs without decrease of volatile and heat sensitive compounds, thus reach high quality food (better nutritional value, colour, taste).
Working principle Using microwave heating [link to DS microwave heating], the energy is transferred to the wet matter with higher efficiency and the moisture is removed faster. This makes that the drying process takes less time and energy [1]. The equipment can be arranged as batch or continuous. The bed should be mixed or rotating. The number of magnetrons depends on conformation and required power level [3].

The microwave heating can be combined with vacuum. [2, 3, 4]

Images
Additional effects Fast start up and shut down procedures.
Important process parameters The properties (like cavity design, power) of microwave drying equipment depend on the raw material (moisture - water activity, structure, origin). We can adjust the power of microwave; structure, size and shape of dried material [4]. See DS Microwave heating
Important product parameters Moisture - water activity, structure, origin.

What can it be used for?

Products All bio-materials can be dried using microwaves. For spices, herbs and other low volume material with highly sensitive components (aromatic, medicinal, colour) microwave drying is especially convenient.
Operations Drying, heating of bio-material. See DS Microwave heating.
Solutions for short comings Need of speeding up the drying process and to reduce losses of volatile compounds as much as possible.

During conventional hot-air drying, some parts of the material can be overheated, leading to decomposition of the heat sensitive compounds or evaporation of the volatile compounds [1].

What can it NOT be used for?

Products Metal containing materials.
Operations Like with classical drying. E.g. too much water is better to separate otherwise.
Other limitations Incorrect conditions can cause colour changes (browning). Should be tested for each product or group of products.
Risks or hazards Strong electromagnetic field. See DS Microwave heating

Implementation

Maturity Microwave heating is a technology commonly used in industry and also in household. Vacuum drying is commonly used too.
Modularity /Implementation Microwave draying replaces other drying techniques. No special changes required.

Other special conditions like vacuum, combination with convective heating can be added. [4, 5]

Consumer aspects No problems expected. Consumers use microwave ovens at home. Moreover this technology results in spices with better properties (colour, flavour, microbiological safety…).
Legal aspects No special aspects comparing with microwave heating.

See DS Microwave heating.

Environmental aspects This technology is environmentally friendly. The efficiency of energy transfer is much higher, than for other heating techniques.

Further Information

Institutes University of Saskatchewan, Universidad Miguel Hernández, Wrocław University of Environmental and Life Sciences, Wageningen UR - FBR
Companies Romill
References [1] Shaw, M.; Meda, V.; Tabil, L. Jr.; Opoku, A Drying and color characteristics of coriander foliage using convective thin-layer and microwave drying. J Microw Power Electromagn Energy 2007, 41 (2), 59-68.

[2] Calín-Sáncheza, Á.; Szumnyb, A.; Figielc, A.; Jałoszyńskic, K.; Adamskid, M.; Carbonell-Barrachinaa, Á. A. Effects of vacuum level and microwave power on rosemary volatile composition during vacuum–microwave drying. Journal of Food Engineering 2011, 103 (2), 219-227

[3] Orsat, V.; Yang, W.; Changrue, V.; Raghavan, G. S. V. Microwave-Assisted Drying of Biomaterials. Food and Bioproducts Processing 2007, 85 (3), 255-263

[4] Figiel, A. Drying kinetics and quality of vacuum-microwave dehydrated garlic cloves and slices. Journal of Food Engineering 2009, 94 (1), 98-104

[5] Sharma, G. P.; Prasad, S. Specific energy consumption in microwave drying of garlic cloves. Energy 2006, 31 (12), 1921-1926

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Created by Radek on 17 April 2012, at 07:15